The invention relates to a speech recognition computer comprising a microprocessor, input and output interfaces and a data bus, in which incoming test signals converted into a digital form are subdivided into segments, and test vectors are assigned to properties of the segments, for which test vectors a distance with reference to reference vectors is computed.
The distance computation is used in speech recognition as a degree of similarity between a part of a speech utterance and a speech reference and represents a central, constantly recurrent task in sample and speech recognition. It requires the longest computation time so that a reduction of the computation time yields a considerable efficiency improvement. In picture processing and sample recognition, it is used for data compression (MPEG).
Up to now, additional, special hardware modules have been used for speech recognition. These modules are used for converting the incoming analog speech signals into digital signals, and for feature extraction in which the characteristic properties of the segmented incoming digitized speech signal are assigned to corresponding vector components. For the test vectors thus formed, the distance to the reference vectors is computed by means of a digital signal processor.
On the other hand, there are software-based speech recognition systems in which the recognition process is performed without any special hardware, i.e. with the system components of a universal computer. The incoming test signals are digitized on, for example, the sound card. The elaborate distance computation is performed on the main processor of the system. This presupposes the use of a very powerful processor and also requires a considerable part of its computation power which is then no longer available for other processes. Generally, the recognition of the spoken text is, however, realized in an off-line mode because a sufficiently powerful processor is not often available.
It is an object of the invention to provide a (universal) arrangement which allows a faster computation of the distances.
This object is solved in that a distance computer and a memory module are provided which are integrated on a common module having at least a data terminal for supplying test vectors and reference vectors and for providing computed distances.
This universal computer system according to the invention allows speech recognition with a conventional microprocessor and its customary peripheral equipment by combination with a memory and an integrated distance computer. The microprocessor is thereby relieved from the elaborate distance computation and its computing power is available for other processes.
To this end, analog data are applied to the computer system via the input and output interfaces, which data, after having been prepared for distance computation, are applied to the memory module with the integrated distance computer.
An additional advantage is the short communication path. Since the data to be compared are directly supplied from the relevant memories to the distance computer, no valuable computation time is lost. The system transfers the test vectors and receives the computed distances. Since the distance computation is locally performed within a memory module, all components of the system, with the exception of the relevant memory module, are available to the system processor for other processes.
Moreover, this integration does not require any data transfers via an external data or address bus for performing the distance computation, i.e. the memory accesses are limited to the internal local memory ranges so that the distance computation is performed directly and within a significantly shorter time. The reference data are loaded into the reference data memory before or at least not during a recognition process step. Also a possible update of this reference data file is performed at non-critical points of time.
A further advantage of this computer system is the possible reconstruction of a computer conceived for normal purposes. A conventional memory module is exchanged for a memory module with an integrated distance computer. This enables the computer system to perform speech recognition processes without any serious limitation of its efficiency.
The integration of a distance computer in a memory module involves further advantages of the optimized memory manufacturing process. Memory modules are produced as logic modules with a higher density of components, resulting in a more optimal utilization of space.
The effectiveness of this integration will be shown by way of an example. In a typical case, the distances of a test vector to, for example, 2000 reference vectors are required every 16 ms. Approximately a data rate of at least 3 Mbyte per second is required for this purpose. A standard signal processor with a clock frequency of 20 MHz would need approximately 12 ms for this purpose. A standard microprocessor requires much more time for this purpose. By integrating the distance computation, this task, performed at the same clock frequency, is reduced to approximately one tenth, i.e. approximately 1.2 ms. The speed gain relates to the optimized addressing, the compact data storage and the shorter data path.
These and other aspects of the invention are apparent from and will be elucidated with reference to the embodiments described hereinafter.